Abstract: A gas turbine engine for an aircraft is disclosed. The gas turbine engine comprises: a combustor, comprising a combustion chamber and a plurality of fuel spray nozzles configured to inject fuel into the combustion chamber, wherein the plurality of fuel spray nozzles comprises a first subset of fuel spray nozzles and a second subset of fuel spray nozzles, wherein the combustor is operable in a condition in which each of the fuel spray nozzles of the first subset of fuel spray nozzles is supplied with fuel at a greater fuel flow rate than each of the fuel spray nozzles of the second subset of fuel spray nozzles, wherein a ratio of the number of fuel spray nozzles in the first subset of fuel spray nozzles to the number of fuel spray nozzles in the second subset of fuel spray nozzles is in the range of 1:3 to 1:6.

Abstract: A gas turbine engine for an aircraft, comprising: a combustor; a fuel-oil heat exchanger arranged to receive fuel and transfer heat from the oil to the fuel so as to raise the fuel temperature to at least 120° C. on entry to the combustor; a fuel recirculation line arranged to recirculate at least some fuel on a fuel flow path from a first point on the fuel flow path to a second point on the fuel flow path, the second point upstream of the first point; and a modulator valve arranged to modulate the flow of fuel along the fuel recirculation line. A method of operating a gas turbine engine is also disclosed.

Abstract: A gas turbine engine has a first subset of fuel spray nozzles and a second subset of fuel spray nozzles. A combustor is operable with the first subset of fuel spray nozzles supplied with fuel at a greater flow rate than each of the second subset of fuel spray nozzles. A ratio of the first subset of fuel spray nozzles to the second subset of fuel spray nozzles is 1:2 to 1:5. A first idle-MTO nvPM emissions index ratio is: EI idle EI max ? TO , where: EIidle is the nvPM emissions index in mg/kg operating at around 7% available thrust; EImaxTO is the nvPM emissions index in mg/kg of the gas turbine engine operating at around 100% available thrust; and the first idle-MTO nvPM emissions index ratio of the gas turbine engine is less than 60. A sustainable aviation fuel (SAF) can be provided to the fuel spray nozzles.

Abstract: A method of operating a gas turbine engine having a lean burn staged combustion system having a combustor in which fuel is combusted. The gas turbine engine includes a fuel-oil heat exchanger arranged to transfer heat between oil and fuel that is provided to the combustor. The method includes transferring heat from the oil to the fuel before the fuel enters the combustor so as to lower the fuel viscosity to 0.58 mm2/s or lower on entry to the combustor at cruise conditions.

Abstract: A gas turbine engine for an aircraft. The gas turbine engine comprising: a rich burn, quick quench, lean burn (RQL) combustor having a number of fuel spray nozzles in the range of 14-22 or a number of fuel spray nozzles per unit engine core size in the range 2 to 6. An MTO nvPM emissions index ratio is defined as: EI maxTO , SAF EI maxTO , FF where: EImaxTO,SAF is the system loss corrected nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for given operating conditions if a fuel provided to the fuel spray nozzles comprises a sustainable aviation fuel (SAF); and EImaxTO,FF is the system loss corrected nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for the given operating conditions if a fuel provided to the fuel spray nozzles is a fossil-based hydrocarbon fuel. The MTO nvPM emissions index ratio of the gas turbine engine is less than 1.

Abstract: An engine system comprises a first fuel store, a second fuel store, an engine arranged to produce mechanical power by combustion or oxidation of a fuel in an engine, a fuel distribution system arranged to deliver fuel from the first and second fuel stores to the engine, the first fuel delivered at a first mass flow rate, the second fuel delivered at a second mass flow rate, the first and second mass flow rates contributing to a total mass flow rate of fuel to the engine; and a control system arranged to control the relative fractions of the total mass flow rate of fuel to the engine represented by the first mass flow rate and the second mass flow rate, based on an engine temperature.

Abstract: A gas turbine engine for aircraft includes a combustor with a combustion chamber and fuel spray nozzles to inject fuel into the combustion chamber. The fuel spray nozzles include a first subset and a second subset of nozzles. Each of the first subset is supplied with fuel at a greater rate than each of the second subset. A ratio of the first subset to the second subset is 1:2 to 1:5. A MTO nvPM emissions index ratio is EI maxTO , SAF EI maxTO , FF . EImaxTO,SAF is nvPM emissions index in mg/kg of the engine when operating at around 100% available thrust if fuel provided to the fuel spray nozzles includes sustainable aviation fuel. EImaxTO,FF is nvPM emissions index in mg/kg of the engine when operating at around 100% available thrust if fuel provided to the fuel spray nozzles is fossil-based hydrocarbon fuel. The MTO nvPM emissions index ratio is less than 1.

Abstract: A method of operating a gas turbine engine including an engine core including a turbine, compressor, combustor to combust a fuel, and core shaft connecting the turbine and compressor; a fan upstream of the engine core; a fan shaft; a gearbox that receives an input from the core shaft and outputs drive to the fan via the fan shaft; a primary oil loop system to supply oil to the gearbox; and a heat exchange system. The method includes controlling the heat exchange system to adjust fuel viscosity to be lower than or equal to 0.58 mm2/s on entry to the combustor at cruise conditions.

Abstract: A gas turbine engine has a first subset of fuel spray nozzles and a second subset of fuel spray nozzles. A combustor is operable with the first subset of fuel spray nozzles supplied with fuel at a greater fuel flow rate than each the second subset of fuel spray nozzles. A a ratio of the first subset of fuel spray nozzles to the second subset of fuel spray nozzles is 1:2 to 1:5. A first idle-MTO nvPM emissions index ratio is: EI idle EI maxTO where: EIidle is the system loss corrected nvPM emissions index in mg/kg operating at around 7% available thrust; and EImaxTO is the system loss corrected nvPM emissions index in mg/kg operating at around 100% available thrust; and the first idle-MTO nvPM emissions index ratio of the gas turbine engine is less than 60. A sustainable aviation fuel (SAF) can be provided to the fuel spray nozzles.

Abstract: A gas turbine engine includes a first and a second subset of fuel spray nozzles. A combustor is operable with the first subset of fuel spray nozzles supplied with fuel at a greater fuel flow rate than each of the second subset of fuel spray nozzles. A ratio of the first to the second subset of fuel spray nozzles is 1:2 to 1:5. A MTO nvPM emissions index ratio is: EI maxTO , SAF EI maxTO , FF . EImaxTO,SAF is the system loss corrected nvPM emissions index in mg/kg operating at around 100% available thrust if fuel provided to the fuel spray nozzles includes sustainable aviation fuel. EImaxTO,FF is the system loss corrected nvPM emissions index in mg/kg operating at around 100% available thrust if fuel provided to the plurality of fuel spray nozzles is fossil-based hydrocarbon fuel. The MTO nvPM emissions index ratio of the gas turbine engine is less than 1.

Abstract: A aircraft gas turbine engine and operation method, the engine including: a staged combustion system having pilot and main fuel injectors, and operates in a pilot-only range wherein fuel delivers to pilot fuel injectors, and a pilot-and-main operation range wherein fuel is delivered to at least the main fuel injectors. The engine further includes a fuel delivery regulator to pilot and main fuel injectors, which receives fuel from a first and second source containing fuels each with different characteristics. The staged combustion system switches between pilot-only and pilot-and-main range operation when in steady cruise mode, the mode defining a boundary between first and second engine cruise operation range. The fuel delivery regulator delivers fuel to pilot fuel injectors during at least part of the first engine cruise operation with different fuel characteristics from fuel delivered to one or both pilot and main fuel injectors the second engine cruise operation range.

Abstract: A gas turbine engine for an aircraft includes a combustor with a combustion chamber and fuel spray nozzles to inject fuel into the chamber. The nozzles include a first and second subset. The combustor is operable so each of the first subset is supplied with fuel at a greater rate than each of the second subset. A ratio of nozzles in the first subset to the second subset is 1:3 to 1:6. A fuel-flow nvPM emissions index ratio is EI idle × W f , idle EI maxTO × W f , maxTO . EIidle is the system loss corrected nvPM emissions index in mg/kg of the engine at around 7% available thrust. EImaxTO is the index at around 100% available thrust. Wf,idle is the rate of fuel to the nozzles in kg/s at around 7% available thrust. Wf,maxTO is the rate of fuel to the nozzles in kg/s at around 100% available thrust. The index ratio is between 0.357 and 8.

Abstract: A gas turbine engine for an aircraft includes a combustor with a combustion chamber and fuel spray nozzles to inject fuel into the chamber. The nozzles include a first and second subset. The combustor is operable so each of the first subset is supplied with fuel at a greater rate than each of the second subset. A ratio of nozzles in the first subset to nozzles in the second subset is 1:3 to 1:6. A thrust nvPM emissions index ratio is EImaxTO/FmaxTO/EIidle/Fidle. EIidle is system loss corrected nvPM emissions index in mg/kg of the engine operating at around 7% available thrust. EImaxTO is system loss corrected nvPM emissions index in mg/kg of the engine at around 100% available thrust. FmaxTO is thrust of the engine at around 100% available thrust. Fidle is thrust at around 7% available thrust. The thrust nvPM emissions index ratio is between 0.0009 and 0.02.

Abstract: A power system for an aircraft includes at least one gas turbine engine arranged to burn a fuel so as to provide power to the aircraft; at least one first fuel tank arranged to be used to power ground-based operation of the aircraft; at least one secondary fuel tank arranged to contain a fuel to be used to power the aircraft in flight; and a fuel manager arranged to control fuel supply so as to take fuel from only the at least one first fuel tank to power at least the majority of ground-based operations.

Abstract: A method of determining one or more fuel characteristics of an aviation fuel suitable for powering a gas turbine engine of an aircraft. The method includes: exposing the surface of a piezoelectric crystal to the fuel; measuring a vibration parameter of the piezoelectric crystal; and determining one or more fuel characteristics of the fuel based on the vibration parameter. Also disclosed is a fuel characteristic determination system, a method of operating an aircraft, and an aircraft.

Abstract: A gas turbine engine includes: a rich burn, quick quench, lean burn combustor having a number of fuel spray nozzles in the range of 14-22 or a number of fuel spray nozzles per unit engine core size in the range 2 to 6. An MTO nvPM emissions index ratio is defined as: EI max ? TO , SAF EI max ? TO , FF where: EImaxTO,SAF and EImaxTO,FF are respectively the nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for the given operating conditions if a fuel provided to the fuel spray nozzles includes a sustainable aviation fuel (SAF) or is a fossil-based hydrocarbon fuel. The MTO nvPM emissions index ratio of the gas turbine engine is less than 1. The gas turbine engine is configured to provide fuel including a SAF to the fuel spray nozzles. Also disclosed is a method of operating a gas turbine engine.

Abstract: A method of operating a gas turbine engine is disclosed, the gas turbine engine including a combustor arranged to combust a fuel and a fuel management system arranged to provide the fuel to the combustor. The fuel management system includes two fuel-oil heat exchangers through which oil and the fuel flow, the heat exchangers arranged to transfer heat to the fuel and comprising a primary fuel-oil heat exchanger and a secondary fuel-oil heat exchanger; and a fuel pump arranged to deliver the fuel to the combustor, wherein the fuel pump is located between the two heat exchangers. The method includes controlling the fuel management system so as to raise the fuel temperature to at least 135° C. on entry to the combustor at cruise conditions.

Abstract: A gas turbine engine for an aircraft includes a rich burn, quick quench, lean burn combustor having 14-22 fuel spray nozzles or 2-6 fuel spray nozzles per unit engine core size. A thrust nvPM emissions index ratio is EI maxTO / F maxTO EI idle / F i ? d ? l ? e . EIidle is the nvPM emissions index in mg/kg of the gas turbine engine operating at around 7% available thrust for given operating conditions. EImaxTO is the nvPM emissions index in mg/kg of the gas turbine engine operating at around 100% available thrust for the given operating conditions. FmaxTO is the thrust of the gas turbine engine at around 100% available thrust in kN. Fidle is the thrust of the gas turbine engine at around 7% available thrust in kN. The thrust nvPM emissions index ratio is greater than 0.09. The gas turbine engine is configured to provide fuel comprising a sustainable aviation fuel to the fuel spray nozzles.

Abstract: A gas turbine engine for an aircraft is disclosed. The gas turbine engine comprises: a combustor, comprising a combustion chamber and a plurality of fuel spray nozzles configured to inject fuel into the combustion chamber, wherein the plurality of fuel spray nozzles comprises a first subset of fuel spray nozzles and a second subset of fuel spray nozzles, wherein the combustor is operable in a condition in which each of the fuel spray nozzles of the first subset of fuel spray nozzles is supplied with fuel at a greater fuel flow rate than each of the fuel spray nozzles of the second subset of fuel spray nozzles, wherein a ratio of the number of fuel spray nozzles in the first subset of fuel spray nozzles to the number of fuel spray nozzles in the second subset of fuel spray nozzles is in the range of 1:3 to 1:6.

Abstract: A power system for an aircraft comprises a gas turbine engine, arranged to burn a fuel in a combustor so as to provide power to the aircraft; a plurality of fuel tanks arranged to contain fuel to be used to provide power to the aircraft; and a fuel manager. A first fuel tank of the plurality of fuel tanks is arranged to contain a first fuel, and a second tank of the plurality of fuel tanks is arranged to contain a second, different, fuel. The fuel manager is arranged to store information on the fuel contained in each fuel tank and to control fuel supply so as to take fuel from the second tank for engine start-up, before switching to the first fuel tank.